A system called a thin client system is known. Thin client systems are configured so that a client is provided with only a minimum of functions and resources, such as applications, and files are managed by a server.
In a thin client system, a client acts as if it actually executes processes and stores data although it is in fact the server that makes the client display results of processes executed by the server or data stored in the server.
When transmitting screen data that is displayed on the client by the server in this way, a transmission delay may sometimes occur due to congestion in the network between the server and the client. This transmission delay of the network causes the drawing of screen data transmitted from the server to be delayed on the client side. Therefore, the response to operations executed on the client side becomes worse.
Incidentally, the following image coding device is used as an example of a technology for reducing the data amount of an image. To share a circuit in which there is an overlap between processes for encoding a moving image and a still image, the image coding device performs quantization capable of processing both the moving image and the still image by changing values of the moving image and the still image stored in a quantization table. For example, there is a video image compression method used in the following graphical user interface. In this compression method, when an input data stream is mixed media data in which multiple media, such as video images, texts, or images, are mixed, after metadata for each medium is obtained, the input data stream is divided into areas corresponding to each medium. Then, by referring to metadata in each medium, this compression method selects a compression algorithm suitable for compressing each area in the input data stream.
Patent Document 1: Japanese Laid-open Patent Publication No. 2000-050263
Patent Document 2: Japanese Laid-open Patent Publication No. 2007-043673
However, with the conventional technology, as described below, there is a problem in that it is not possible to prevent an increase in the amount of data transmission.
In general, the amount of encoded data obtained by performing compression encoding on a moving image can be smaller than that obtained by performing compression encoding on a still image; however, this relationship is not always established. For example, if a screen is a line drawing of a simple background, the amount of screen data may sometimes be smaller when using a compression format for a still image suitable for the line drawing than when using a compression format for a moving image that is advantageous for compressing an image containing many colors. In such a case, if the compression format for the moving image is continuously used, because the compression ratio of the screen data decreases when compared with a case in which the still image compression format is used, the amount of data transmission increases. However, with the conventional technology, because it is not possible to change the compression format selected when an image is input during a process, an increase in the amount of data transmission is not prevented.